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importance to regulating behavior. The pituitary secretes hormones that influence our responses
to pain as well as hormones that signal the ovaries and testes to make sex hormones. The
pituitary gland also controls ovulation and the menstrual cycle in women. Because the pituitary
has such an important influence on other glands, it is sometimes known as the “master gland.”
Other glands in the endocrine system include the pancreas, which secretes hormones designed to
keep the body supplied with fuel to produce and maintain stores of energy; the pineal gland,
located in the middle of the brain, which secretes melatonin, a hormone that helps regulate the
wake-sleep cycle; and the thyroid and parathyroid glands, which are responsible for determining
how quickly the body uses energy and hormones, and controlling the amount of calcium in the
blood and bones.
The body has two triangular adrenal glands, one atop each kidney. Theadrenal glands produce
hormones that regulate salt and water balance in the body, and they are involved in metabolism,
the immune system, and sexual development and function. The most important function of the
adrenal glands is to secrete the hormones epinephrine (also known as adrenaline)
andnorepinephrine (also known as noradrenaline) when we are excited, threatened, or stressed.
Epinephrine and norepinephrine stimulate the sympathetic division of the ANS, causing
increased heart and lung activity, dilation of the pupils, and increases in blood sugar, which give
the body a surge of energy to respond to a threat. The activity and role of the adrenal glands in
response to stress provides an excellent example of the close relationship and interdependency of
the nervous and endocrine systems. A quick-acting nervous system is essential for immediate
activation of the adrenal glands, while the endocrine system mobilizes the body for action.
The male sex glands, known as the testes, secrete a number of hormones, the most important of
which is testosterone, the male sex hormone. Testosterone regulates body changes associated
with sexual development, including enlargement of the penis, deepening of the voice, growth of
facial and pubic hair, and the increase in muscle growth and strength. The ovaries, the female sex
glands, are located in the pelvis. They produce eggs and secrete the female
hormones estrogen and progesterone. Estrogen is involved in the development of female sexual
features, including breast growth, the accumulation of body fat around the hips and thighs, and